Roofing underlayments are typically installed over the roof deck and under the primary roof covering or overlayment, which can be asphalt shingles, metal shingles, or metal roofing, tiles such as Spanish or slate tile, wood shakes, concrete, slate, etc. The underlayment provides a secondary moisture barrier to protect the roof deck and building interior from moisture that may penetrate through the primary roof covering. Commercially effective underlayments must maintain their strength and integrity even after exposure to the elements. Underlayments are used both in new construction and in re-roofing projects.
It is known in the waterproofing art to combine a pre-formed waterproofing membrane, such as a rubberized bitumen/oil layer, with a carrier support sheet or film, and to utilize this as an underlayment. The carrier support film may comprise a variety of materials, such as rubber, plastic, and/or metal, or combinations of the same. The use of metals is desirable, for example, to improve dimensional stability of the support film, which is subjected to oil migration from the oil-plasticized bitumen layer. It has also been desirable to employ cross-laminated plastic films, such as high density polyethylene, for improved stability of the carrier support sheet.
Such pre-formed waterproofing membrane laminates are considered “sheet-like” because they are sufficiently flexible that they can be rolled up and transported after manufacture to the job site where they are unrolled and installed on the building surface. This kind of membrane laminate, useful as an underlayment on sloped roofs, is commercially available from Grace Construction Products (W. R. Grace & Co.-Conn.) under the name “ICE & WATER SHIELD” (a registered trademark of W. R. Grace & Co.-Conn.) The underlayment is applied to the roof deck before installation of the overlayment. The function of the membrane underlayment is to seal around roofing fasteners and to protect against damage from ice dams and wind-driven rain. Another commercially available example of an underlayment is “TRI-FLEX 30”, (a product also available from Grace Construction Products) which is spun-bonded polypropylene coated with a thin layer comprising U.V. stabilized polypropylene on both of its surfaces.
In addition to its water shedding capabilities, an important characteristic of a roofing underlayment is its skid or slip resistance. Since roofing applicators must walk on the underlayment during roofing installation, the exposed surface should have a sufficiently high coefficient of friction, even when wet, so as to minimize or prevent an applicator from slipping when walking or standing on the surface. Skid resistant underlayments are disclosed, for example, in U.S. Pat. No. 5,687,517, U.S. Pat. No. 6,308,482, US 2003/0215594, US 2004/0127120 and US 2007/0044397. Other types of membranes or sheets containing particles or filler materials of various types are disclosed, for example, in US 2004/0192130, U.S. Pat. No. 5,496,615, U.S. Pat. No. 4,994,328 and U.S. Pat. No. 6,500,520.
It is also desirable that the roofing underlayment be rollable for ease of transportation and handling, and be readily unrollable, ideally by a single person, for application. However, maintaining unrollability while providing sufficient skid resistance can be problematic, particularly where the skid resistance is due to the tackiness or stickiness of the walking surface. That is, the same tackiness that is advantageously used to provide skid resistance can make it difficult or impossible to unroll the underlayment, particularly if the unrolling is to be carried out by only one person.
It is also desirable that the underlayment be light in weight, i.e. low weight per unit area. Lightweight provides for easier transportation to the roofdeck and easier installation. Some underlayments comprise a heavy layer of a large particulate that provides for a heavyweight membrane. It therefore would be desirable to provide a lightweight roofing underlayment having excellent skid resistance while maintaining unrollability.
Furthermore, it is desirable that good skid resistance is maintained or even improved after exposure outdoors to the degradative effects of UV and thermal oxidative exposure. Roofing underlayments may be expose for 6 months or more prior to application of a wearing surface such as shingles. During this period the underlayment will be exposed to sunlight and the temperature of the membrane may reach as high as 180° to 220° F. (82°-104° C.) for a dark colored membrane or 120° to 140° F. (49°-60° C.) for a highly reflective white membrane.